This invention relates to a point-to-multipoint network having a center transmitting signals to several nodes.
In point-to-multipoint networks, e.g. in a cable distribution network with or without reverse channel, signals, such as cable television signals and/or telephone signals (xe2x80x9ccablephonexe2x80x9d), are generally transmitted from a center over two separate optical fiber links to several nodes in such a way that each of the nodes receives signals from both links. Each node serves a coaxial cable network with a plurality of terminals. Such a network structure is known from the journal xe2x80x9ctelecom reportxe2x80x9d of Siemens AG, No. 3/1996, pages 10 to 13.
The separate optical fiber links are provided to ensure that in the event of a disturbance, caused, for example, by a cable break or by insufficient amplification, it is not possible for individual nodes to receive no signals or only signals of reduced quality. In each node, the incoming signals on the two links are detected by means of two detectors, and only the signal with the higher level is routed onward via a switch.
A disadvantage of such networks is that both optical fiber links must constantly be operated at a high signal level, whereby much power is wasted, which also increases the aging rate of the network.
In the network disclosed in DE 19650088, two optical fiber links connected to a center end in a switching assembly which routes signals onward only if a disturbance is detected on one of the two optical fiber links. In this manner, a reserve link is activated on the occurrence of a disturbance, so that the performance of the network can be optimized for the trouble-free case. Disadvantages are that a separate switching assembly is needed, and that in the event of a disturbance, the supply of signals to nodes depends on the proper operation of the switching assembly.
It is therefore an object of the invention to provide a network in which an optimized mode of operation is made possible both in the trouble-free case and on the occurrence of a disturbance.
This object is attained by a point-to-multipoint network according to the invention which characterized in that it comprises two nodes designed as subcenters which are connected to a center via respective main trunk lines and make the signals received from the center available on reserve lines. By activating the reserve lines only if disturbances are present on the main trunk lines, power can be saved. The occurrence of a disturbance in a main trunk line is detected autonomously by each node concerned. In this manner, the nodes can control the reception and forwarding of the signals autonomously and independently of additional control equipment, such as a central switching assembly, and the reserve line is activated only on the occurrence of a disturbance.
Futher advantages features of the invention will be apparent from the description below and the appended claims.